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Thursday, December 1, 2011

New Study Throws Dark Matter Finding Into Question

It's amazing how many people make a good living searching for non-existent stuff like Dark Matter.

Maybe they should look for something more tangible, like extraterrestrials. Many scientists already know ETs exists, they don't want the general public to know, might interfere with their research on Dark Matter, and the illusive (also non-existent god particle, Higgs boson) .

A new study of dark matter, the mysterious hidden stuff thought to
pervade the universe, casts doubt on a previous finding that offered hope that
dark matter had finally been seen.

In 2008, a European-Russian satellite called
Payload for Antimatter Matter Exploration and Light nuclei Astrophysics (PAMELA) discovered a strange overabundance of particles called positrons, which are the antimatter
counterpart to electrons. Matter and antimatter, which have the same mass but
opposite charges, destroy one another when they meet.

According to theory, when a particle of dark matter collides with its
antiparticle, they annihilate, unleashing a burst of energy and exotic
particles. Dark matter is thought to make up 98 percent of all matter in
the universe and 23 percent of its total mass and energy. Scientists have yet to
directly detect invisible dark matter, but its existence is inferred based its
gravitational pull on regular matter.

The positrons found by PAMELA were thought
to be the products of dark matter annihilation with antimatter, and scientists were
hopeful that the tantalizing discovery could prove the existence of the elusive
dark matter.

But a new study has raised more questions about PAMELA's discovery.
Researchers at the Kavli Institute for Particle Astrophysics and Cosmology
(KIPAC) at Stanford University
in California confirmed the overabundance of positrons, but when they did not
see a sudden drop-off of this excess beyond a certain energy level, they knew something was wrong.

"If the antimatter we measure is coming from the annihilation of dark matter
particles, then the positron excess should drop off fairly suddenly at an energy
level that corresponds with the mass of the dark matter particle," study co-author Stefan Funk,
an assistant professor of physics at Stanford University, said in a
statement.

"Some have concluded that this altogether rules out dark matter as a source
of the antimatter we're measuring," Funk said. "At the very least this means
that if the positrons are coming from dark matter annihilation, then dark matter
particles must have a higher mass than allowed by the PAMELA measurement."

But the results are not necessarily a definitive strike against the finding,
the researchers said.

"We're taking an observational point of view
and simply reporting the data that we observe," Vandenbroucke said. "However, I know that articles are
already appearing that say our result likely

rules out the dark matter
interpretation. Personally, I think that is too strong of an
interpretation."

Additional observations will be needed to
settle the debate, the researchers said. One instrument in particular, the
antimatter-hunting Alpha Magnetic Spectrometer (AMS), is expected to yield helpful
results.

NASA's space shuttle Endeavour carried the AMS experiment to the
International Space Station in May, where it was installed on the exterior of
the complex. It has been operating ever since. This detector should be able to
collect more precise data at higher energies, Vandenbroucke said.

"AMS has a very large magnet in its detector and so can naturally and very
easily distinguish between electrons and positrons," Funk said. "That experiment
will most likely be able to make a final statement on this. It's something we
are all eagerly awaiting."

Funk and Vandenbroucke used NASA's Fermi Gamma-ray Space Telescope, which
studies the highest energy forms of light. Since the telescope is designed to
detect neutral light particles, called photons, it does not have a magnet to
separate negatively charged electrons and positively charged positrons.

The researchers were forced to improvise, but luckily a natural magnet exists
close to home: Earth. The planet's magnetic field naturally bends the paths of
charged particles that almost continuously rain from space, they explained.

The scientists then studied geophysical maps of Earth and calculated how the planet filters
out charged particles seen by the telescope, in a novel approach at the
intersection of astrophysics and geophysics.

"The big takeaway here is how valuable it is
to measure and understand the world around us in as many ways as possible,"
Vandenbroucke said. "Once you have this basic scientific knowledge, it's often surprising how that knowledge can be useful."

The researchers detailed their results in a
paper submitted to the journal Physical Review Letters.